Shaun Edwards: 'Wales is like a giant Wigan, the warmth of the welcome, the passion for their rugby.' Photograph: David Davies/PA

We were due to meet on a chilly terrace at the back of the Vale of Glamorgan hotel that has been base camp for Wales since the age of Graham Henry, only six years past but fully half a dozen coaches ago. The Jail of Glamorgan, as it was known in an age of irreverence BS. Before Shaun.

In front of the hotel lies the car park where once Steve Hansen, five coaches back, leant on the bonnet of Dafydd James's car and, being a wily old Kiwi policeman, worked out that the wing had broken curfew. James was sent homeward, an example to others in an age of indiscipline. BS.

'Couldn't you find somewhere a little colder?' said Shaun Edwards, stepping on to the terrace, glowing bald on top, chin dug into his chest. He was fresh from the gym. 'I eat like a horse,' he confessed, 'but still have the drive to work it off, luckily.'

He dug his hands into his blue-grey Welsh Rugby Union anorak and lowered his head even further. If you can see a lot of the 41-year-old's pate and feel slightly discomfited by the way he seems to stare at you from beneath his eyebrows, it is because he wears his chin well tucked in. Perhaps it helped him survive all those years in Wigan. Never leave anything hanging out. Anything jutting at jaw level might just be too tempting for passing elbows.

Self-defence for an animated small man in rugby league might have been the first step in developing the science of defence in union. Edwards is now defence coach of Wales and Wasps, or Wasps and Wales, a job-share that perhaps he alone could contemplate. Animation and stamina do not seem to be a problem.

Warren Gatland, who was appointed by the WRU to succeed Gareth Jenkins after the World Cup, invited Edwards to reform their coaching partnership. They had worked together at Wasps until Gatland returned to Waikato in New Zealand in 2005.

It was not an entirely simple decision for Edwards. First, he had to clear it with Ian McGeechan at Wasps. In truth, his director of rugby had long ago acknowledged that the ambition and drive that consumed Edwards would have to be accommodated. McGeechan gave his blessing.

Then, he had to square it with the Wasps players, several of whom - Phil Vickery, Simon Shaw, James Haskell, Tom Rees and Paul Sackey - would be facing Wales for England on the opening day of the Six Nations. A job is a job, they said. Go for it.

Except it was not the only job. He was also offered the job of coaching the England Saxons, the national second team. 'The safest thing would have been to take the Saxons job,' said Edwards. 'Well, the safest thing would have been to stay in rugby league. But sometimes... sometimes you have to chase the adventure.'

Edwards joined Gatland in Wales. But it all took time. I asked him what it was like when he finally came face to face with his new charges, after so many weeks of wondering where he was destined. 'I told them I - we - were there to help them. That if I criticised them it was only constructive. That we were all in this together. That there would be nothing personal in anything we might say.'

And then, according already to legend, he started screaming in their faces. According to Tom Shanklin in his newspaper column, few of the players had come across anything like this ever before. Not that they minded it. Far from it. But it was novel.

'Well, for starters, I don't scream in anyone's face. I don't swear or abuse anyone. I suppose sometimes I just want to get my point across.'

The image of vigorous communication was reinforced in the closing moments of Wales's victory at Twickenham. On the steps leading down to the field appeared Edwards, shouting and gesticulating as the seconds ticked away.

'I simply wanted Lee Byrne to get back into position. There we were, in the lead and on the attack. But we had to think what might happen if England suddenly broke out. We didn't want our full-back to be in the line. We wanted him to be back where he belonged.

'This shouting thing. Take Lee, for example. I obviously had a message for him at that particular moment. He understood immediately. And then I had another word with him about the lines and angles he was running in attack. A quiet word, mind you. And look what he did against Scotland to make Shane Williams' first try.

'Another example would be Gavin Henson and our set-piece defence. He's been quick to grasp what we're expecting. He's been outstanding. I said to Warren: "You don't have to tell them twice, do you?" '

In the time Edwards has been in rugby union the notion of what to do when your side is not in possession of the ball has changed. First, there's the art of tackling.

If he did not invent the blitz defence he certainly reinvented it to suit the 15-a-side game. It is characterised by extreme aggression and the speed of the advancing tacklers. Sure, there are slightly less unsubtle elements with regard to positioning and repositioning, but the abiding impression is that the defences constructed by Shaun Edwards are ferocious.

He denied there was anything new about the importance of tackling. 'Defence is not something totally different from attack. It's not like American football where there's a completely different team for defence. In rugby, when you don't have the ball you're in defence. Simple as that. As important as that.

'I've been looking at the statistics and talking to loads of people here about the days when Wales had great attacking teams. To people like Clive Rowlands who was coach in the 1970s. He said that when Wales had the best defence in the Five Nations they won the title. Or put it like this, it didn't matter how many points those Welsh teams scored, if they slipped to third in the defence rankings, they did not win the championship. The importance of defence is nothing new.'

But the notion of using defence as a form of attack, as important as the scrum or line-out to secure possession, has never been developed to such an extent as it is in the modern game.

He paused. 'It's true that defence is only as good as the appetite for tackling. The lust for it.'

On Saturday, unbeaten Wales take on Italy. How clear is Edwards's picture of his new team? How much has it shifted? After 35 minutes of the game against England, the player who never contemplated anything other than victory with Wigan was a worried coach.

'I thought at that moment we were going to go away from Twickenham without showing what we could do. That would have been bad. So I went from that sense of growing disappointment to what our second-half performance made me feel. Well, before that really. That period of defence just before half-time was all-important. The fortitude shown was tremendous.'

Changes were still made for the game against Scotland. Mark Jones was dropped for one game because, it seemed, he had stayed on the floor for a few seconds when he was not actually unconscious. Alix Popham was left out for giving away penalties.

And more changes have been made for Italy. James Hook and Mike Phillips, brilliant at times in two games, mismanaged the third quarter against Scotland. Dwayne Peel and Stephen Jones start now. The front row has been replaced. Players no longer live in any sort of comfort zone. 'Nobody's dropped,' countered Edwards. 'We just want to have a look at a lot of players. Let them have their go. They're all straining at the leash,' he said. 'But let's not get carried away. It's Italy next. Nobody's looking any further than that.'

I mentioned the head-to-head, potentially titanic, between Wales captain Ryan Jones and Italy's No 8, Sergio Parisse. 'We might have to work out how to do a number on that Parisse.' He made it sound a bit chilling. 'He seems to be the one their game revolves around.'

He admired Italy's second half against England. And Ireland's against France. 'There's been a lot of interesting things so far. Some weird things.'

And Wales suddenly look, what, models of fortitude and commonsense? 'Wales is like a giant Wigan,' he offered, not exactly by way of agreement. 'The warmth of the welcome, the passion for their rugby, the sheer... It's a bit...'

Bonkers? 'Maybe.' And with that he marched off the cold terrace. I wished him well. 'As long as we don't kick the ball off the field,' he said from the doorway. 'We kick it into touch, the crowd claps. We coaches are throwing our hands up.'

He was gone. Shaun Edwards and Greater Wigan are getting on just fine.